Patient monitoring of various physiological parameters of a patient is important to a wide range of medical applications. Oximetry is one of the techniques that has developed to accomplish the monitoring of some of these physiological characteristics. It was developed to study and to measure, among other things, the oxygen status of blood. Pulse oximetry—a noninvasive, widely accepted form of oximetry—relies on a sensor attached externally to a patient to output signals indicative of various physiological parameters, such as a patient's constituents and/or analytes, including for example a percent value for arterial oxygen saturation, carbon monoxide saturation, methenoglobin saturation, fractional saturations, total hematocrit, billirubins, perfusion quality, or the like. A pulse oximetry system generally includes a patient monitor, a communications medium such as a cable, and/or a physiological sensor having light emitters and a detector, such as one or more LEDs and a photodetector. The sensor is attached to a tissue site, such as a finger, toe, ear lobe, nose, hand, foot, or other site having pulsatile blood flow which can be penetrated by light from the emitters. The detector is responsive to the emitted light after attenuation by pulsatile blood flowing in the tissue site. The detector outputs a detector signal to the monitor over the communication medium, which processes the signal to provide a numerical readout of physiological parameters such as oxygen saturation (SpO2) and/or pulse rate.
High fidelity pulse oximeters capable of reading through motion induced noise are disclosed in U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952 5,769,785, and 5,758,644, which are assigned to Masimo Corporation (“Masimo”) and are incorporated by reference herein. Advanced physiological monitoring systems can incorporate pulse oximetry in addition to advanced features for the calculation and display of other blood parameters, such as carboxyhemoglobin (HbCO), methemoglobin (HbMet), total hemoglobin (Hbt), total Hematocrit (Hct), oxygen concentrations and/or glucose concentrations, as a few examples. Advanced physiological monitors and corresponding multiple wavelength optical sensors capable of measuring parameters in addition to SpO2, such as HbCO, HbMet and/or Hbt are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006, titled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208, filed Mar. 1, 2006, titled Noninvasive Multi-Parameter Patient Monitor, assigned to Masimo Laboratories, Inc. and incorporated by reference herein. Further, noninvasive blood parameter monitors and optical sensors including Rainbow™ adhesive and reusable sensors and RAD-57™ and Radical-7™ monitors capable of measuring SpO2, pulse rate, perfusion index (PI), signal quality (SiQ), pulse variability index (PVI), HbCO and/or HbMet, among other parameters, are also commercially available from Masimo.
The accuracy of patient monitors, generally, and oximeter systems, specifically, can be critical to the care and diagnosis of a patient being monitored. Therefore, proper calibration of patient monitors and noninvasive sensors is desirable.